The invention relates to a fuel injection system for an internal-combustion engine, having a high-pressure pump for feeding the fuel into a dual-fluid nozzle, and also means for supplying a second fluid to the dual-fluid nozzle.
As known, peak combustion chamber temperatures, and consequently nitrogen oxides, can be reduced by selectively injecting water into the combustion chamber while combustion takes place.
EP 0 282 819 A2 discloses, for example, a fuel injection system designed as a dual-fluid system, in which water fed by a feed pump is stored during an injection pause in a pressure space of the dual-fluid nozzle and is injected with the subsequently supplied diesel fuel into the combustion chamber for reducing nitrogen oxide emission. The respective quantity of water is determined by a control valve in an additional fluid line. During the storing of the water, an automatically opening pressure valve in the high-pressure pump provides relief in the high-pressure line.
It is the object of the invention to improve the fuel injection system in such a way that a feed pump for the additional fluid of relatively low pumping capacity is used independently of the level of the system pressure in the high-pressure line and that, after injection, a rapid pressure build-up can be reestablished in the high-pressure line.